This invention relates to an apparatus for transferring disks such as semiconductor wafers each having a center hole from one cassette of a conventional type to another cassette of a similar conventional type but having a different pitch.
Semiconductor wafers are fragile or otherwise easily rendered useless by contamination or abrasion. Therefore, they are usually carried in a cassette for transporting from one work station to another during processing. A cassette used for such a purpose is shaped generally like a box or a cage with a bottom opening, having walls with grooves at a constant pitch as disclosed, for example, in U.S. Pat. Nos. 4,311,427 issued Jan. 19, 1982, 4,471,716 issued Sept. 18, 1984, 4,493,418 issued Jan. 15, 1985 and 4,743,156 issued May 10, 1988. A plurality of (typically 25) disks are positioned in such a cassette, maintained vertically and parallel to one another. In order to save space, wafers in such a cassette are separated from one another only by a small distance of typically about a quarter of an inch. When the wafers undergo a washing process, however, individual wafers cannot be washed effectively if they are aligned so close to one another. For this reason, another cassette is usually provided for such a purpose with wafer-supporting grooves on the walls separated by a larger distance, say, about one-half inch. Thus, wafers which have been brought to a washing station are taken out in a piece-by-piece fashion from their usual cassette used generally for their transportation and transported into this specially provided cassette with grooves spaced wider apart. Transferring wafers thus from one cassette to another with a different pitch is a troublesome procedure, whether done manually or by a robot.